System and method of transmission and reception of progressive content with isolated fields for conversion to interlaced display

ABSTRACT

Systems and methods of coding progressive content with isolated fields for conversion to interlaced display are provided. Some systems and methods may find use in, for example, digital video compression systems and methods. Film material may be encoded as video material with an intended field polarity and an explicit 3:2 pull-down operation for interlaced display (e.g., a 30-frames-per-second display).

RELATED APPLICATIONS

[0001] This application makes reference to, claims priority to andclaims benefit from U.S. Provisional Patent Application Serial No.60/351,182, entitled “Method for Enabling Transmission and Display ofEncoded Compressed Film Material in a Video Bit Stream” and filed onJan. 22, 2002; U.S. Provisional Patent Application Serial No.60/384,234, entitled “Method for Enabling Transmission and Display ofEncoded Compressed Film Material in a Video Bitstream” and filed on May30, 2002; and U.S. Provisional Patent Application Serial No. ______,entitled “Method for Enabling Transmission and Display of EncodedCompressed Film Material in a Video Bit Stream” and filed on Jan. 17,2003.

INCORPORATION BY REFERENCE

[0002] The above-identified United States patent applications are herebyincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

[0003] In countries that use 525-line interlaced display systems suchas, for example, the United States and Canada, television video signalsare sampled and transmitted at approximately 59.94 fields per second(fps). For such countries, digital television video streams aregenerally encoded and transmitted by using a particular Moving PicturesExperts Group (MPEG) standard (e.g., MPEG-2 Video) at approximately29.97 frames per second (FPS).

[0004] Hereinafter, an integral value of fps or an integral value of FPSmay be an approximation including, within its scope, a range ofequivalent values. Thus, for example, the expression 30 FPS may be usedto refer to rates such as, for example, approximately 29.97 FPS orapproximately 30 FPS. Furthermore, the expression 24 FPS may be used torefer to rates such as, for example, approximately 23.976 FPS orapproximately 24 FPS. Similarly, the expression 60 fps may be used torefer to rates such as, for example, approximately 59.94 fps orapproximately 60 fps.

[0005] Film material produced at 24 FPS is routinely converted to 60 fpsin many applications. Broadcast networks usually encode and transmitmovies that were originally filmed at 24 FPS and not at 60 fps. However,at the receiver, the decoded video at 24 FPS is often converted to 60fps for interlaced display. A conventional process for converting 24 FPSto 60 fps sampling includes the Telecine Process (named after theoriginal type of machine used to perform the conversion from film tovideo). It is also known as the 3:2 pull-down process. The TelecineProcess inserts repeated fields derived from the original film frames insuch a way that 5 video frames (i.e., 10 fields) are produced for every4 original film frames. FIG. 1 illustrates one example of a process 12that performs a 3:2 pull-down. The original film sequence 10 filmed at24 FPS is converted to a video sequence 14 at 30 FPS, or equivalently 60fps. A mechanism of handling 3:2 pull-down for film material in digitalvideo systems is usually referred as film mode.

[0006] The Telecine Process or 3:2 pull-down process is supported in theMPEG-2 Video compression standard. When using the MPEG-2 Video standardwith the film mode, the frame rate encoded in the sequence header is 30FPS for interlaced display, even though the video is actually coded as a24 FPS film sequence. The encoder also conveys, to the decoder, properdisplay timing based on the frame rate of 30 FPS. The flagstop_field_first and repeat_first_field in the picture coding extensionheader are used for indicating how a picture should be displayed. Thesetwo flags are mandated as MPEG-2 syntax elements that are carried allthe time and are followed by decoder. However, such inflexibility maynot be desirable, particularly, when the type of display device can varyfrom, for example, an interlaced television to a progressive monitor.Furthermore, the encoder does not know the type of display employed atthe decoder end.

[0007] In MPEG-2 Video elementary streams, the flags top_field_first andrepeat_first_field are used to indicate the current film state. Fourfilm states A, B, C and D are illustrated in FIG. 1. The four possiblefilm mode states are generally repeated in the same order every fourpictures. FIG. 2 illustrates the mapping between the film states andthese 3:2 pull-down flags in MPEG-2 Video.

[0008] In MPEG-2, the decoder generally follows the top_field_first andrepeat_first_field flags to display film state B and D frames for threefield times to re-construct the 3:2 pull-down pattern. The decoderre-displays the first field to create the third field. This is because,in the 3:2 pull-down algorithm, the first field is repeated every otherpicture to convert film material at 24 FPS to video mode at 30 FPS. Filmstate A and C pictures are displayed for only two field times. A filmmode sequence of four pictures will therefore be displayed as a total of10 field times. In this way, the decoded video is displayed at thecorrect video picture rate of 30 FPS

[0009] In MPEG-2, the flags top_field_first and repeat_first_field alongwith the frame rate can also be applied to derive Decoding Time Stamps(DTS) and Presentation Time Stamps (PTS) for some pictures. The flags(i.e., top_field_first and repeat_first_field) are used to achieveproper timing for decoding and displaying the coded 24 FPS film materialto generate output video at 30 FPS.

[0010] However, for compressed video formats without these flags (orsimilar flags), the 3:2 pull-down process or the film mode is supportedin a different manner and not supported by, for example, new videocompression standards (e.g., MPEG-4 Advanced Video Coding (AVC)) as wellas with some of the existing video transport standards (e.g., MPEG-2Systems).

[0011] In formats other than those following the MPEG-2 Systems standard(i.e., ISO/IEC 13818-1), decoding time and presentation time may beindicated via syntax elements that differ from DTS specifications andPTS specifications found in MPEG-2 Systems. As used herein, the termsDTS and PTS may be interpreted as including, within their meaning,decoding time or buffer removal time and presentation time or displaytime, respectively, regardless of how they may be encoded in thebitstream.

[0012] Further limitations and disadvantages of conventional andtraditional approaches will become apparent to one of ordinary skill inthe art through comparison of such systems with some aspects of thepresent invention as set forth in the remainder of the presentapplication with reference to the drawings.

BRIEF SUMMARY OF THE INVENTION

[0013] Some aspects of the present invention may relate to a system anda method of encoding progressive content with isolated fields forconversion to interlaced display. Some applications within the scope ofthe present invention may find use, for example, in digital videocompression systems and methods.

[0014] In one embodiment, the present invention may provide an encoderthat is adapted to encode film material as video with an intended fieldpolarity and an explicit 3:2 pull-down operation for interlaced display(e.g., a 30 FPS display). An isolated field with the intended fieldpolarity (e.g., top field) may be coded between two frames to achieve3:2 pull-down for coding the film material. The polarities of all fieldsof all frames may be inferred from the field polarities of the isolatedframes since the field polarities alternate for normal interlaceddisplay of video. Frames do not have to indicate field polarities;however, they may do so in video coding standards that support theindication of field polarity of frames. The field polarities of theframes may be implied by the polarities of the isolated fields.

[0015] In another embodiment, unlike in MPEG-2 Video, for example, thepresent invention may provide that DTS and PTS may be generated for bothcoded frames and fields in the encoder. The encoder may insert isolatedfields as appropriate to achieve the desired decoding and displaytiming, for example, according to the result of a 3:2 pull-down process.In cases where the input to the encoder is the result of a 3:2 pull-downprocess, the encoder may encode progressive frames with interspersedisolated fields in a manner similar to the content that is received bythe encoder. In the decoder, for coded pictures (e.g., frame pictures orfield pictures) that do not have associated DTS and PTS in the stream,their decoding and presentation times may be derived from the decodingand presentation times of previous pictures (e.g., frame frames or fieldpictures) by using the frame rate or the field rate indicated in thestream. In one example, the decoding and presentation times may bederived from the decoding and presentation times of previous pictures byusing only the frame or the field rate indicated in the stream.

[0016] In yet another embodiment, unlike the MPEG-2 film mode flags, forexample, the present invention may provide that its use does notcomplicate the video buffer model in the Hypothetical Reference decoderportion of the video standard, since the frame rate and buffer removaltimes are consistent with or without the use of film mode encoding.

[0017] These and other features and advantages of the present inventionmay be appreciated from a review of the following detailed descriptionof the present invention, along with the accompanying figures in whichlike reference numerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 illustrates an embodiment of a 3:2 Pull Down process.

[0019]FIG. 2 illustrates an embodiment of a mapping between film modestates and 3:2 pull-down flags.

[0020]FIG. 3 illustrates an embodiment of a pattern of frames and fieldsaccording to the present invention.

[0021]FIG. 4 illustrates an embodiment of a system that facilitates thedisplay of video according to the present invention.

[0022]FIG. 5 illustrates an embodiment of a system that facilitates thedisplay of video according to the present invention.

[0023]FIG. 6 illustrates a flowchart showing an embodiment of a processthat facilitates the display of video according to the presentinvention.

[0024]FIG. 7 illustrates a flowchart showing an embodiment of a decodingprocess according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0025] Some aspects of the present invention may relate to a system anda method that encodes progressive content with isolated fields forconversion to interlaced display. Some applications within the scope ofthe present invention may find use in, for example, digital videocompression systems and methods. Some embodiments according to thepresent invention may be suitable for use in and compatible with someMPEG standards (e.g., an MPEG-4 AVC standard as described in, forexample, document JVT-E146d37ncm.doc, entitled “Joint VideoSpecification (ITU-T Rec. H.264|ISO/IEC 14496-10 AVC)”, incorporatedherein by reference in its entirety).

[0026] Some aspects of the present invention may relate to providing asystem and a method that realizes a 3:2 pull-down process or a film modefor at least some video compression systems and methods. Someembodiments according to the present invention may be suitable for usein and compatible with some MPEG standards (e.g., MPEG-4 AVC) includingsome existing video transport standards (e.g., MPEG-2 Systems).

[0027]FIGS. 4 and 5 show respective block diagrams illustratingembodiments of systems that facilitate the display of video according tothe present invention. Referring to FIG. 4, a transmitter 40 may becoupled to a receiver 50 via a network 60. The receiver 50 may, in turn,be coupled to a display 90. The transmitter 40 may include, for example,an encoder 70. The receiver 50 may include, for example, a decoder 80.FIG. 5 shows another embodiment for the receiver 50 including, forexample, a transport processor 100 and a multimedia processor 110. Inone embodiment, the transport processor 100 may be coupled to thenetwork 60 and to the multimedia processor 110. The multimedia processor110 may be coupled to the display 90 and may include, for example, thedecoder 80. Although illustrated as part of the multimedia processor110, the decoder 80 may be separate from the multimedia processor 110.Furthermore, although illustrated as separate components, the transportprocessor 100 and multimedia processor 110 may be integrated at least inpart. In one embodiment, the transport processor 100 and the multimediaprocessor 110 form a single integrated chip. The present inventioncontemplates other degrees of integration and separation.

[0028]FIG. 6 illustrates a flowchart showing an embodiment of a processthat facilitates the display of video according to the presentinvention. In operation, in step 120, the encoder 70 of the receiver 50may encode, for example, film material as video material with anintended field polarity and with an explicit 3:2 pull-down operation forinterlaced display via the display 90. In step 130, the encoder 70 mayinsert one or more isolated fields with the intended field polarity(e.g., a top field or a bottom field) between two frames to achieve 3:2pull-down for coding the film material. The field polarities of thefields in all of the frames may be inferred from the field polarities ofthe isolated frames. In one embodiment, this may be because, forexample, the field polarities alternate for normal interlaced videodisplay. In step 140, the bitstream (e.g., a video bitstream) may betransmitted over a network (e.g., cable television, satellite, digitaltelevision, broadcast, Ethernet, Internet, wireless network, etc.) tothe receiver 50. In step 150, the transport processor 100 may parse thereceived bitstream and may output the parsed bitstream to the multimediaprocessor 110. In step 160, the multimedia processor 110, which mayinclude, for example, the decoder 80, may extract or may determinetiming information and may decode the bitstream. If not present, thetiming information for a particular frame or a particular field may bedetermined from the timing information from one or more previous framesor one or more previous fields. The multimedia processor 110 may use aframe rate or field rate indicated in the bitstream to determine timinginformation for a particular frame or a particular field. In step 170,the decoded bitstream may then be displayed on the display 90 using, forexample, the extracted or determined timing information. For example,the multimedia processor 110 may use the time stamp information indetermining the timing for displaying pictures (e.g., frame pictures,field pictures, etc.)

[0029] Compressed digital video may include, for example, coded framesand coded fields. According to the MPEG-2 Video standard (i.e., ISO13818-2), coded fields occur in pairs (i.e., an isolated field is notallowed between two frames). Furthermore, each picture of a film modesequence in MPEG-2 is always coded as a frame. In one embodiment, theisolated fields may be used to code some pictures in film mode. Inanother embodiment, the present invention may be used with the MPEG-4AVC standard. An isolated field with the indicated field polarity (e.g.,top field or bottom field) may be coded between, for example, two framesto achieve the 3:2 pull-down process for coding film material. Theframes may or may not have the field order indicated explicitly. Theorder of the fields of the frames may be implied, for example, by thepolarity of the isolated fields.

[0030] The film mode states correspond, for example, to frame types A,B, C and D of the 3:2 pull-down process as illustrated in FIGS. 1 and 2.An embodiment of the operation of an encoder according to the presentinvention is illustrated in FIG. 3. For film mode state A, a picture 20is coded as a frame whose top field precedes its bottom field in time.For film mode state B, a first picture 22 is coded as a frame whose topfield precedes its bottom field in time followed by a second picture 24coded as a field. The coded field in the second picture 24 representsthe top field of the film mode state B. In one embodiment, it ispredicted from the top field of the preceding frame picture in state B.For film mode state C, a picture 26 is coded as a frame whose bottomfield precedes its top field in time. For film mode state D, a firstpicture 28 is coded as a frame whose bottom field precedes its top fieldin time followed by a second picture 30 coded as a field. This codedfield represents the bottom field of the film mode state D. In oneembodiment, it is predicted from the bottom field of the preceding framepicture in state D.

[0031] Some embodiments of encoding and decoding methods for film modeaccording to the present invention may be well suited for supportinginterlaced display. FIG. 7 shows a flowchart illustrating an embodimentof a decoding process according to the present invention. In query 180,the decoder determines whether or not the decoder selects 3:2 pull-downcontent (e.g., 30 FPS). The encoder may explicitly encode a 24 FPS filmsequence into a 30 FPS (or, equivalently, 60 fields per second) videosequence for transmission. If the decoder chooses to use 3:2 pull-downformat (e.g., the decoder may be coupled to an interlaced display with aformat and a frame rate compatible with those indicated in thebitstream) then, in step 190, the encoded video sequence may be directlydecoded and presented on the display without using the flags such as,for example, top_field_first and repeat_first_field as in MPEG-2 Video.The interlaced format of the content is displayed in step 200. If thedecoder chooses not to use the 3:2 pull-down format then, in step 210,the decoder detects and removes the isolated fields. The decoder maychoose not to use the 3:2 pull-down format if, for example, the decoderis coupled to a progressive display, or if a display has a differentformat or frame rate from those indicated in the bitstream. Suchisolated fields may be detected by the decoder since, for example, thefield is isolated and the field is predicted from a previous frame. Instep 220, the coded frames may then be displayed in a progressive formator the content may be converted to match the display which may be, forexample, interlaced with a different size or a frame rate from the rateresulting from the use of the isolated fields.

[0032] Even when a different video encoding specification from MPEG-2 isused to compress the video, it may still be desirable to use the MPEG-2Systems specification (e.g., Transport Stream) to transmit the encodedbit stream, due to the wide use of equipment implementing thisspecification and its proven performance and reliability. It may also bedesirable to maintain current investments in the transmission anddelivery infrastructure.

[0033] In accordance with the present invention, film material may beencoded with the indicated frame rate being the interlaced display framerate (e.g., 30 FPS) without using flags such as, for example,top_field_first and repeat_first_field. The time-stamping process forthe decoding time stamp (DTS) and the presentation time stamp (PTS) inMPEG-2 Systems may be slightly different than that for MPEG-2 Video. ForMPEG-2 Video, DTS and PTS are typically generated for coded frames inthe encoder by examining the corresponding film states. In an MPEG-2decoder when encountering frames that do not have DTS and PTS coded, thedecoding and presentation times generally are derived from the decodingand presentation times of previous frames in combination with the framerate and the repeat_first_field flag. However, unlike MPEG-2 Video, insome embodiments according to the present invention, DTS and PTS may begenerated for coded pictures in the encoder without knowing the filmmode states of the pictures. Also, unlike MPEG-2 Video, in someembodiments according to the present invention, DTS and PTS may begenerated for either coded frame pictures or field pictures in which thefield picture may be isolated (e.g., not necessarily in pairs). When adecoder encounters a picture without DTS and PTS coded in the stream,the decoder can infer the correct decoding and presentation times forthat picture from the decoding and presentation times of previouspictures (e.g., frame pictures or field pictures) in combination withonly using frame rate or field rate, without using a repeat_first_fieldflag or the equivalent.

[0034] Unlike the MPEG-2 film mode flags, some embodiments according tothe present invention do not complicate the video buffer model in theHypothetical Reference Decoder portion of the video standard, since theframe rate and buffer removal times are consistent with or without theuse of a film mode.

[0035] In some embodiments, the present invention may not indicate anyfield polarity of the frames when the isolated fields are included. Thefield polarity of all of the frames may be determined by the polaritiesof the isolated fields.

[0036] While the present invention has been described with reference tocertain embodiments, it will be understood by those skilled in the artthat various changes may be made and equivalents may be substitutedwithout departing from the scope of the present invention. In addition,many modifications may be made to adapt a particular situation ormaterial to the teachings of the present invention without departingfrom its scope. Therefore, it is intended that the present invention notbe limited to the particular embodiment disclosed, but that the presentinvention will include all embodiments falling within the scope of theappended claims.

What is claimed is:
 1. A system for facilitating a display of a video,comprising: an encoder adapted to encode a film material as a video witha field polarity and a 3:2 pull-down operation for an interlaced displayformat, wherein the encoder inserts an isolated field with the fieldpolarity.
 2. The system according to claim 1, wherein the encoderinserts the isolated field between a first frame and a second frame toachieve 3:2 pull-down for coding the film material.
 3. The systemaccording to claim 1, wherein the encoder encodes a 24 frames-per-secondfilm sequence as a 30 frames-per-second video sequence for transmission.4. The system according to claim 1, wherein the encoder encodes the filmmaterial into a bitstream.
 5. The system according to claim 4, whereinthe bitstream comprises an alternate field polarity scheme.
 6. Thesystem according to claim 5, wherein a polarity of a particular field isdetermined from a polarity of the isolated field.
 7. The systemaccording to claim 1, wherein the encoder is adapted to generate a timestamp for a particular picture without knowledge of a film mode state ofthe particular picture.
 8. The system according to claim 1, wherein theencoder is adapted to generate a decoding time stamp (DTS) or apresentation time stamp (PTS) for a particular picture without knowledgeof a particular film mode state of the particular picture.
 9. The systemaccording to claim 1, wherein the encoder is adapted to generate a DTSor a PTS for each encoded frame.
 10. The system according to claim 1,further comprising: a decoder coupled to the encoder via a network. 11.The system according to claim 10, wherein the decoder is adapted todetermine a decoding time or a presentation time for a particularpicture based upon at least one DTS or at least one PTS for a previouslydecoded picture.
 12. The system according to claim 11, wherein thedecoder is adapted to determine the decoding time or the presentationtime for the particular picture using a particular frame rate or aparticular field rate.
 13. The system according to claim 12, wherein theparticular frame rate or the particular field rate is indicated in abitstream comprising encoded film material received from the encoder.14. The system according to claim 10, wherein the decoder is adapted todetect and to remove the isolated field.
 15. The system according toclaim 10, wherein the decoder is adapted to decode and to present avideo sequence without using a film mode flag.
 16. A method forfacilitating a display of a video, comprising: encoding a sourcematerial as a video material with a field polarity and a 3:2 pull-downoperation for an interlaced display format; and inserting an isolatedfield with the field polarity between two frames to achieve 3:2 pulldownfor coding the source material.
 17. The method according to claim 16,wherein the source material is encoded without specific knowledgeconcerning film mode states of the source material.
 18. The methodaccording to claim 16, wherein a particular field polarity of aparticular field is determined based upon at least the field polarity ofthe isolated field.
 19. The method according to claim 16, furthercomprising: encoding progressive content with one or more of theisolated fields for conversion into the interlaced display format. 20.The method according to claim 16, wherein the encoded source materialforms a bitstream.
 21. The method according to claim 16, furthercomprising: generating a time stamp for a coded frame or a coded field.22. The method according to claim 16, further comprising: determining atime stamp for a particular coded picture based upon a value of aprevious time stamp of a previous coded picture.
 23. The methodaccording to claim 22, further comprising: determining a time stamp fora particular coded picture based upon a frame rate or a field rate. 24.The method according to claim 23, further comprising: indicating theframe rate or the field rate in a bitstream comprising the encodedsource material.
 25. The method according to claim 16, furthercomprising: providing a time stamp for a particular picture withoutknowledge of a film mode state of the particular picture.
 26. The methodaccording to claim 16, further comprising: detecting and removing theisolated field.
 27. The method according to claim 16, furthercomprising: decoding and presenting a video sequence without using afilm mode flag.